Morphotypes
 

Naked lobose amoebae are polymorphic; a single cell can adopt very different shapes, especially when it is stationary or moves in a non-coordinated manner, often changing the direction of locomotion.
Based on the locomotive form of a naked lobose amoeba, Smirnov and Goodkov (1999) and Smirnov and Brown (2004) distinguish a number of basic morphotypes, which can be very helpful in describing and identifying naked lobose amoebae. These morphotypes are displayed below:

     
Polytactic amoeba  

1 Polytactic
Polypodial amoebae with large, distinctive, well pronounced pseudopodia, which consist both of granuloplasm and hyaloplasm. They actively participate in the movement of the amoeba. Pseudopodia can be numerous ore restricted to only two or three.

Genera:
Amoeba
Chaos
Pseudothecamoeba

     
Orthotactic amoeba  

2 Orthotactic
Monopodial amoebae, subcylindrical in cross section, always with lateral and/or dorsal wrinkles. Cells may retain trailing remnants of small lateral pseudopodia, which do not participate in locomotion.

Genera:
Amoeba
Chaos

 

     
Palmate morphotype  

3 Palmate
Polypodial amoebae; with numerous pseudopodia of approximately equal size, which are formed from the basal part of the body; wide fasciculate uroid.

Genera:
Polychaos
Deuteramoeba

     
Morphotype monotactic  

4 Monotactic
Monopodial, elongate, amoebae, which are subcylindrical in cross section, with a smooth surface, without any lateral or dorsal wrinkles. They show a steady cytoplasmic flow. This shape has also been described as limax-form.

Genera:
Trichamoeba - Hydramoeba - Polychaos - Parachaos - Metachaos - Saccamoeba - Cashia - Glaeseria - Hartmannella - Nolandella - Amoeba

     
Monotactic amoeba  

5 Rhizomonotactic
Amoebae in rapid locomotion monopodial, with distinct adhesive uroid (arrow) and usually with large hyaline cap.

Genus: 
Rhizamoeba




 

     
Flabellate morphotype  

6 Flabellate
Flattened, usually irregular, triangular cells with prominent anterior hyaloplasm and uneven frontal edge. Cell never forms distinct subpseudopodia from the frontal hyaloplasm, though it may be divided into distinct lobes with deep clefts.

Flabellate amoebae are always very flattened and expanded, and change shape rapidly. Some species have distinct adhesive uroidal filaments in locomotion.

Genera:
Stachyamoeba
Rosculus
Guttulinopsis
     
Flamellian morphotype  

7 Flamellian
Amoeba flattened and expanded, or only the frontal part is flattened. Subpseudopodia, lobes and waves are formed from the frontal hyaloplasm. Body shape in locomotion may vary from elongate to semicircular or crescent shape.

Some species have a cuticle, covering the dorsal surface only, and belong also to the lens like morphotype. Interestingly, alternative locomotive forms of at least two Rhizamoeba species belong to this morphotype.

Genera:
Flabella
Gocevia

     
Lens-like morphotype Cochliopodium  

8 Lens shaped
Amoeba lens shaped, dorsal surface covered by a flexible tectum or cuticle, visible as punctations; with hyaline subpseudopodia from under this cover or numerous spineolate subpseudopodia on the ventral surface.
The tectum is easily recognizable light microscopically in larger species, but is invisible in smaller species. The cuticle is more difficult to see; it appears as a mucose layer under DIC optics, but is clearly visible on wrinkled areas of the cell where it is perpendicular to the focal plane.

Amoebae of genus Cochliopodium and Paragocevia belong to this morphotype.

     
Striate morphotype Thecamoeba  

9 Striate
Amoebae flattened, oblong or rounded with several nearly parallel dorsal folds. These longitudinal ridges always dominate during locomotion. Less regular wrinkles may also appear but are never numerous.

Amoeba of this type belong to genus Thecamoeba:
Thecamoeba quadrilineata
Thecamoeba striata
Thecamoeba similis

 

     
Rugose morphotype Thecamoeba  

10 Rugose
Amoebae flattened, oblong or rounded, with numerous irregular dorsal wrinkles. Dorsal folds, if present, are irregular and not parallel in arrangement.

Amoebae of this morphotype are soil amoebae, belonging to genus Thecamoeba. There are many poorly described verrucosid amoebae in older literature.
Thecamoeba sphaeronucleolus
Thecamoeba verrucosa
Thecamoeba terricola

     
Lanceolate morphotype  

11 Lanceolate
Amoebae lancet like, with lateral flatness, without folds or wrinkles. However, they do display a distinctive lateral flatness, which makes them appear “hat like” in cross section.

One genus Paradermamoeba

     
Lingulate morphotype  

12 Lingulate
Amoebae always flattened in cross section, oblong, smooth, always without any folds or wrinkles, but one or two small lateral wrinkles may appear temporarily. In contrast with species of lanceolate morphotype they do not display lateral flatness of the cell.

Species of this morphotype belong to:
Dermamoeba
Sappinia diploidea
Platyamoeba

 

     
Fan shaped morphotype  

13 Fan shaped
Amoebae flattened, fan shaped, semi circular or spatulate amoebae, without subpseudopodia. Always with a wide frontal hyaline zone, which is normally smooth or forms small dorsal lobes, waves or/and temporary wrinkles.
Edge always smooth or slightly waved, but never lobate. No adhesive uroidal structures.

Species of this morphotype are amongst the most common in all habitats and belong to genera:
Vannella
Platyamoeba
Pessonella

     
Mayorella morphotype  

14 Mayorellian
Amoebae elongate or irregularly triangular, with distinct narrow antero lateral border of hyaloplasm; blunt conical or mamilliform subpseudopodia; small dactylopodia, if present (rarely).

During locomotion amoebae of these morphotype are less flattened and many of them have a tendency to form longitudinal dorsal ridges. Most species adopt an oblong shape during rapid locomotion and move “as a whole”, without distinct pseudopodia and subpseudopodia.

Species of this morphotype to genus:
Mayorella

     
Dactylopodial morphotype  

15 Dactylopodial
Amoebae usually irregularly triangular, with distinct wide anterior hyaline border or frontal hyaline zone. With dactylopodia of different length, mostly from the frontal hyaloplasm. Conical and mammiliform subpseudopodia are very rare, and may be formed only temporarily.

Amoebae of this morphotype produce characteristic finger-shaped hyaline subpseudopodia (dactylopodia) and only rarely (and temporarily) conical or mamilliform pseudopodia.
In locomotion they have an expanded frontal hyaline zone. Large specimens have a strong tendency to produce dactylopodia from the dorsal surface of the cell also.

Genera: Korotnevella

     
Dactylopodial morphotype  

16 Acanthopodial
Amoebae usually irregularly triangular, with short, sharp, tapering, pointed, sometimes furcate, hyaline subpseudopodia, formed both from the anterior hyaloplasm and from the lateral and dorsal parts of the cell.

Group 1: Genus Vexillifera: subpseudopodia are never branched and never noticeably pointed, subpseudopodia mostly from the frontal hyaline area. 
Group 2: Genera Acanthamoeba and Protacanthamoeba:  amoebae usually have branched subpseudopodia (acanthopodia) which may have pointed tips.
Group 3: Genera Echinamoeba, Filamoeba and Comandonia: amoebae produce many very fine, spinelike subpseudopodia and may even resemble filose amoebae.
Photomicrograph: Yana Eglit

     
Branched morphotype  

17 Branched
Amoebae flattened, branched with anastomosing lobose pseudopodia (loboreticulopodia) and poorly coordinated movement. Pseudopodia never contain granules and never form an expanded network. Cytoplasmic flows never distinct or shuttle like.
Apparently, all amoebae of this morphotype, if disturbed, may adopt a monotactic like form for a short time (in contrast with the plasmodium of slime molds), but (with the exception of Rhizamoeba spp.) they do not maintain this form during locomotion.

Genera:
Leptomyxa - Rhizamoeba - Gephyramoeba

Photomicrograph: Angie Opitz

     
Eruptive morphotype  

18 Eruptive
Monopodial amoebae, markedly eruptive in locomotion.
Eruptions may be more or less pronounced, but are always visible. These amoebae have variable, but generally monopodial shape but are never as flattened as amoebae of flabellate morphotype.

 

Each morphotype isn’t restricted to specific species or genera. Most polytactic amoebae adopt the orthotactic locomotive form during active, fast, movement and belong to the orthotactic morphotype as well.

 

An excellent guide to the morphology and indentification of naked amoebae is: Smirnov, A. V., Brown, S. (2004): Guide to the study and identification of soil amoebae. Protistology 3:148–190.